1. Field of the Invention
The present invention relates to method for the handling of especially fragile tape-supported thin sections of tissue specimens prior to staining and mounting processes and, more particularly, to expedite and simplify the positive, safe transfer to and support of such sections on microscope slides for such processes.
2. Brief Description of the Invention
Very thin slices of animal and plant tissues are prepared for many diferent kinds of microscopic studies by sectioning with a microtome. While the tissue may be cut fresh, the soft and compliant nature of most fresh tissue makes the cutting of undistorted thin sections very difficult. Often, the tissue is cut on a freezing microtome or in a cryostat at temperatures below 0.degree. C. (32.degree. F. ), the hardness of the frozen water within the tissue allowing sections as thin as a few micrometers to be cut relatively easily. As these frozen sections are brittle and friable, they are difficult to handle and process further. To simplify sectioning of tissue, a number of procedures have been developed which produce a block of supported tissue which has superior sectioning properties and produce high quality, relatively easy-to-handle tissue sections. Such procedures typically involve: (1) Fixation of the tissue in a solution which insolubilizes and hardens the natural polymers of which tissue cells are composed; (2) dehydration of the tissue through a series of water-miscible (e.g. an alcohol) and then paraffin or plastic-monomer-miscible (e.g., toluene or xylene) solvents; (3) infiltration of the tissue by melted paraffin or monomer solution; and (4) embedding by freezing the paraffin or polymerizing the monomer to form a solid polymer. Reference is made to Staining Methods, J. F. A. McManus and R. W. Mowry (P. B. Hoeber, Inc., N.Y. 1960) and to Techniques for Electron Microscopy, D. Kay, Ed. (Blackwell Sci. Publ., Oxford, England, 1965) pp. 166-212.
However, there are occasional specimens which remain difficult to section. As the section is cut from the tissue, parts of the cut section tend to fragment and fall from the cut section, or fall from the section as it is removed from the microtome. Reference is made to the following which describe procedures for facilitating the cutting and handling such difficult-to-cut tissue sections:
1. A. Palmgren, Nature, Vol. 174, p. 46, (1954) describes the use of a pressure-sensitive adhesive tape as a sectioning aid for the cutting of very large, hard or brittle specimens. A piece of adhesive tape is applied to the surface of a specimen, either frozen or embedded in a paraffin block, supported in a microtome. Thus, the section, when cut, is thus supported by the applied tape. The quality of the uncompressed section of hard, brittle and friable tissue thus produced can be far superior to that of a conventional section of the same block of tissue. However, following Palmgren, processing such a section while it remains on the tape, or transferring it to a glass slide (to permit it to be processed thereafter in conventional fashion) involved elaborate, timeconsuming and inconvenient methods which can also damage the section.
2. W. E. Beckel, Nature, Vol. 184, p. 1584 (1959) describes the use of Scotch brand No. 810 cellulose-acetate-backed adhesive tape in the process described by Palmgren above. The tape-mounted sections were applied, section-side down on wet conventionally albuminized glass slides. After thorough drying, which requires at least a few hours, the adhesive backing, the adhesive layer and the paraffin were all dissolved in tetrahydrofuran for 30 minutes, leaving only the section adhering to the glass slide and available for further processing by conventional techniques. Alternatively, chloroform for 2 minutes, followed by xylene for 30 minutes, can be used for dissolving the adhesive backing, the adhesive layer and the paraffin. Beckel also described a "more rapid method" which used a film of albumin and a solution of 2 per cent celloidin in methyl benzoate or ethyl alcohol to "cement" the section to the glass slide, followed by 1 minute in chloroform and 10 minutes in xylene to complete the treatment.
3. D. S. Gowers and R. E. Miller Nature, Vol. 190, p. 425 (1961) attempted to repeat Beckel's method but found that, with available Scotch brand No. 810 tape, the adhesive could not be dissolved, and with the best alternate available tape, Tuck brand No. 200, safe removal of the tape without damaging the section in solvent took from 1 to 10 hours.
4. R. P. Wedeen and H. I. Jernow Am. J. Physiol., Vol. 214, p. 776, (1968) used cyanoacrylate (Eastman 910 "superglue" ) to attach adhesive-tape-supported frozen sections to radioautographic (photographic) plates. The cyanoacrylate is initially liquid, but polymerizes to a solid when pressed into a thin film. As the cyanoacrylate polymer is soluble in xylene and other processing solvents which would cause the section to float free, it is not useful for conventional staining procedures.
The present invention deals, at least in part, with the mounting of adhesive-tape-supported, cut-tissue sections by permanent bonding to a microscope slide by a rapid and convenient method, the bonding material being such as not to be affected by or interfere with any of the treating processes to which such section is subsequently subjected or with the subsequent microscopic examination of the fully-treated section.